Trident Scholar Abstracts 2012

An Autonomous Surface Vessel (ASV) is essentially an unmanned boat that has been programmed to undertake a specific mission or to exhibit a specific behavior. A Swam is some number of these craft that are somehow coordinated to collectively undertake a mission or task. This Trident Project focuses on the development of a controller for the coordination of a swarm of Autonomous Surface Vessels under mission and environmental constraints. For this research project, we first improved an existing degree of freedom ASV model. This model of a 360 metric ton patrol boat contains nonlinear hydrodynamics for the vessel's surge, sway, roll, and yaw motions. The model was modified to take into account environmental conditions including wind, waves and currents. Additionally, the control inputs of the model (propeller thrust, and desired ruder angle) were adapted for easier integration with a swarm-level controller and other nonholonomic motion constraints were applied to increase model fidelity.

We then integrated this model into a simulated swarm of ASVs. It is the intention that this model will more accurately depict nonlinear vessel dynamics than did models used in previous ASV swarm studies. The swarm controller enables the ASVs to travel in a formation with the intent of protecting and escorting a hypothetical asset. To provide flexibility, the controller is capable of modifying overall formation shape and mission parameters in response to varying environmental conditions. The Atlantic Center for the Innovative Design and Control of Small Ships, a research initiative sponsored by the Office of Naval Research, plans to apply techniques and methods developed in this study towards the construction and testing of a physical swarm of ASVs.

This Trident project employs direct writing with an atomic force microscope (AFM) to fabricate simple graphene-based electronic components like resistors and transistors at nanometer-length scales. The goal is to explore their electronic properties and the feasibility of using this technique for the manufacturing of graphene-based electronics. The graphene devices are expected to be denser and faster, and to dissipate heat more efficiently than current silicon-based transistors. Here we fabricate conducting nanoribbons of graphene using two different AFM techniques, thermochemical nanolithography (TCNL) and thermal dip-pen nanolithography (tDPN). TCNL involves flowing current through an AFM tip to provide precise local heating to an insulating graphene substrate (graphene oxide or graphene fluoride). The heat reduces the substrate into a material known as reduced graphene oxide/fluoride (rGO/F) which exhibits electric properties close to those of pristine graphene. These nanoribbons can be used to fabricate nanoscale electronic components such as resistors, capacitors, and transistors. Compared to other attempts to produce graphene-based devices, this technique is simple, does not involve solvents or other complicated fabrication steps, and allows for the exact placement of the devices on the wafer. The thermal dip pen nanolithography uses a heated AFM tip dipped in polymer which leaves a layer of masking material on the surface of pristine graphene. When the graphene sheet is functionalized through fluorination and thereby rendered insulating, the narrow layer of polymer locally protects the graphene underneath. The properties of the devices produced using these two fabrication methods are compared by measuring their electrical current-voltage characteristics.

Measurement of Ship Air Wake Impact on a Remotely Piloted Aerial Vehicle

One of the components of Naval Aviation is the ability to launch and recover helicopters from the flight decks of conventional warships. In order to ensure the safety of the pilots and the ship’s crew, launch and recovery wind limits are set for each helicopter and ship combination. Currently, these limits are determined through flight testing at sea, which can be expensive, risky, and difficult to schedule. Because the Naval Academy’s YPs are relatively large vessels with a similar superstructure and deck configuration to that of a cruiser or a destroyer, air wake data can be collected that corresponds well with that of modern naval warships. A dedicated YP has been modified with a flight deck and hangar structure to produce air wakes similar to that on a modern destroyer.

This project, an addendum to the original ship air wake project, uses an instrumented remotely piloted helicopter with a 4.5 ft diameter rotor to measure the helicopter’s interaction with the YP’s turbulent air wake. Currently, a T-Rex 600E Super Pro remote-controlled helicopter has been fitted with a GPS data logger and an inertial measurement unit. As the helicopter maneuvers through regions in the ship’s air wake where there is a steep velocity gradient, the inertial measurement unit records a noticeable change in the helicopter’s flight through its tri-axial accelerometers and gyroscopes. At any time, the relative position of the helicopter can be determined by a differential GPS calculation comparing the GPS position of the helicopter with that of a reference position on the ship. Combining these two measurement systems, the locations of sharp gradients in the air wake can be mapped relative to the ship (accurate within one rotor diameter of the helicopter model) and compared with CFD simulations of similar wind-over-deck configurations. Data collected from underway flight operations will lead to a macro-scale validation of CFD analysis of the ship’s air wake at locations distant from the flight deck.

An Adaptive H-Infinity Algorithm for Jitter Control and Target Tracking in a Directed Energy Weapon

In recent years the Office of Naval Research has undertaken the challenges posed by directed energy weapons with the creation of the Directed Energy Weapons Program. The program identified five main fields of focus necessary for creating an effective directed energy weapons system, with control being one of them A laser travels at the speed of light, redefining the type of targeting and tracking method used. It must remain on target, at a precise location, for the entire duration of fire to achieve maximum effectiveness. Directed energy weapons, like all mechanical systems, are subject to vibrations which cause the beam to deviate from the intended aimpoint. With on-target precision being such an important aspect, the slightest vibrations in the directed energy system can cause tremendous problems. Beam stability is needed at the micro- to sub-micro- radian level. This project will address two primary challenges of a directed energy weapon: platform jitter and target tracking. First, to control platform jitter, an adaptive controller was created to actively identify and attenuate tonal frequencies of the platform. With a stable beam, a second controller tracks and targets the laser onto a moving target. The results show a significant reduction in induced jitter demonstrating a potential to significantly increase the effectiveness of directed energy weapons.

Solving systems of polynomial equations has a wide range of applications, from statistical economics to robot motion planning. Sometimes it's helpful just to count the number of solutions to the system of equations. In enumerative geometry we count the number of geometric objects that satisfy a specific system of polynomial constraints. The goal of this project is to count the number of hyperplane arrangements sharing the same combinatorial type that also satisfy a list of geometric conditions. We develop explicit formulas for families of generic hyperplane arrangements in any dimension, as well as for families of pencils in the projective plane.

Our main result is that there are 166,695 different braid arrangements of six lines containing eight fixed points in general position. Moreover, we determine the characteristic numbers of three generic lines. Using these numbers, we solve all possible intersection problems involving three generic lines. In order to compute these enumerative results, we use both combinatorial methods and intersection polynomials in the Chow Ring. The enumerative results give deep information about the moduli space of arrangements with a fixed intersection type. Mnew's Universality Theorem shows these spaces, the points of which are themselves individual arrangements, can be unfathomably complicated; however, we use Macaulay2 to determine explicit minimal generators of the ideal of the Zariski closure of the moduli space of the braid arrangement.

We also develop code for the computer algebra package SAGE to compute the multivariate Tutte polynomial. We expect that these is a connection between evaluations of the Tutte polynomial and the solutions to enumerative problems. After extensive computer trials in SAGE, we found relations valid for generic arrangements and pencils, but in general the precise connection is also enumerate the number of realizable rank-3 matroids. We devise SAGE scripts to determine the independent sets of the matroid associated with each arrangement. Finally, we use Geogebra to animate deformations of arrangements in order to study singularities of the moduli space.

Boat-generated wake wash can lead to erosion of loose bank sediments and the destruction of fragile aquatic habitats. Although various studies have been done to quantify the magnitudes of boat wakes and their associated energy, there lacks a single model which can universally predict wave heights across different vessel sizes, boating speeds and hull forms. The goal of this research is thus to develop a single, unifying equation model capable of predicting boat-generated wave heights given a set of pre-defined parameters

A remote web-based camera was used to document vessel traffic over a section of the Severn River from October – December 2011. Vessels were tracked using the Horn-Schunck Optical Flow method, and boat parameters, such as boat length, speed, and distance of its sailing line from shore, were measured using the Computer Vision Toolbox in Simulink & MATLAB. Continuous wave height measurements were concurrently recorded by an underwater wave gage (Nortek AWAC). Using Fourier transforms, the wave records were filtered to extract maximum wave heights generated by the passing boats from wind-generated waves present in the background.

The project’s goal is to compile a general database of boat parameters and their associated wave heights that will allow us to identify relationships present. From this database, we develop a unified equation model capable of quantifying vessel-wakes magnitudes. With the unified equation model, we hope to aid future theories investigating wave energy and sediment resuspension relationships in developing effective solutions for shoreline management.

The U.S. Navy has shown an interest in the development of small reciprocating piston engines for Unmanned Aerial Vehicles (UAVs). These engines provide reduced fuel consumption relative to small gas turbine engines, but substantially increase weight. Weight is of significant importance to UAVs to allow sufficient range and loitering times. Carbon fiber composites offer strength-to-weight benefits over the metal components currently used in piston engines. However, composite components have more restrictive operating temperatures. None of the known previous efforts aimed at integration of composites into engines has focused on air-cooled engines and on their potential benefits for UAVs.

A small, single-cylinder air-cooled gasoline engine was chosen as a convenient test platform and surrogate for an air-cooled UAV engine. Steady-state temperature profiles were measured internally and externally. Carbon fiber composite test specimens were tested for strength at a comparable range of temperatures to demonstrate thermal viability. A thermal model was constructed to enable prediction of expected temperatures with variable amounts of carbon fiber integration. Wall strain was measured and modeled on the stock engine and used to design a composite crankcase and connecting rod. These composite components were integrated and tested successfully on the engine and indicate a potential weight savings of approximately 80% per component. The results of these tests were used to calibrate the stress and thermal models, providing a more robust predictive tool for more extensive carbon fiber integration in the future.